Antioxidants for mineral oil lubricants and compositions containing the same



Patented Apr. 18, 1950 ANTIOXIDANTS FOR MINERAL LUBRI- CANTS AND COMPOSITIONS CONTAINING THE SAME Herschel G. Smith, Wallingford, and Troy L. Cantrell, Lansdowne, Pa., and John G. Peters, Audubon, N. J., assignors to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application March 10, 1948, Serial No. 14,168

13 Claims.

1 This invention relates to antioxidants for mineral oil lubricants and compositions containing the same, and more particularly, it relates to addition agents for mineral oil lubricants which inhibit the oxidative deterioration of said lubricants.

In the lubrication of internal combustion engines of all types, particularly when severe operating conditions are encountered, plain mineral lubricating oils oftenprove unsatisfactory in service because of the oxidative deterioration of the oil, with the attendant deposition on the engine surfaces of varnish, gum or sludge. Furthermore, many lubricating oil compositions which may be highly satisfactory for the lubrication of other mechanisms have been found wholly unsuitable for use as turbine oils.

The formation of varnishes, gums and sludges on engine surfaces is due at least in part to oxidation effects on mineral lubricating oils. In turbine oils the problem of oxidation is further aggravated, because in normal use turbine oils rapidly become contaminated with water.

It is an object of this invention, therefore, to provide an addition agent for mineral oil lubricents which will inhibit the oxidative deterioration of such lubricants.

It is further an object of this invention to provide improved mineral oil lubricant compositions which are remarkably stable against oxida- 'tion under service conditions.

These and other objects are accomplished by the present invention wherein an addition agent for mineral oil lubricants is prepared by condensing p-hydroxydiphenyl (p-phenylphenol), N- dimethylaniline and formaldehyde in the presence of an activated clay catalyst, and recoverin: the condensation product. The condensation product so obtained is a light-colored product which, when added to mineral oil lubricants, confers a remarkable stability against deterioration by oxidation. Such condensation products and mineral oil lubricant compositions containing them are believed to be novel and are considered parts of our invention. Contrary to what may be expected from the nature of the reactants, we do not obtain highly-condensed, insoluble resinous products. On the contrary, when the above reactants are condensed in accordance with our invention, there are obtained v necessary.

'2 light-colored condensation products which are nonresinous and which are readily soluble in mineral oils.

In performing the condensation the reactants are mixed and heated to a maximum temperature of 350 F. We have found that if the temperature of 350 F. is exceeded to any substantial extent, the condensation product formed tends to be resinous and insoluble. The preferred temperature for the condensation ranges from to 280 F. The proportions of the reactants may vary over a relatively wide range. For each moi of parahydroxydiphenyl there is employed 4 to 9 mols of N-dimethylaniline and 4 to 9 mols of formaldehyde. Ordinarily, it is preferred to use from 5 to 10 per cent by weight of the activated clay catalyst, based on the total weight of the reactants. However, smaller amounts, as low as 1 per cent by weight, and larger amounts, as high as 20 per cent by weight, may also be employed; but larger amounts than about 10 Per cent by weight are ordinarily not In lieu of formaldehyde any formaldehydeyielding compound, such as paraformaldehyde, dioxymethylene and trioxymethylene may be employed. In such case, the amount of formaldehyde-yielding compound used is based on the equivalent number of mols of formaldehyde yielded within the range of proportions of formaldehyde set forth hereinabove. Accordingly, as used in the appended claims, the term formaldehyde is intended to include formaldehydeyielding compounds as well as formaldehyde itself.

Various activated clay catalysts may be employed in accordance with our invention. Such materials are well known in the art and comprise a natural clay, such as bentonite, fullers earth, floridin and smectite, which has been acid treated in order to activate the clay. These materials are described in U. S. Patent 1,898,165, for example.

In preparing our new addition agent, the reactants and catalysts are placed into a. reaction vessel which is then closed and the mixture heated with agitation until all of. the formaldehyde or formaldehyde-yielding compound has been consumed. At this time the water which is formed as a result of the condensation is re- 3 moved, preferably under vacuum, and the dehydrated condensation product is then filtered to remove the activated clay catalyst. In some instances, it is desirable to prepare our new addition agent in a concentrate in a mineral lubricating oil which may then be diluted down with additional oil tothe concentration desired in the final lubricating composition. In such instances, the mineral lubricating oil may be added in a suitable amount, say in a weight equal to the weight of reactants, to the reaction mixture in the reaction vessel, and the condensation product obtained will then be a concentrated solution of the addition agent in the mineral lubricating oil.

The condensation products obtained in accordance with our invention are liquids or crystalline solids. While we do not desire to be bound by any theory as to the reaction or reactions involved or the chemical composition of the products, we believe that in view of the multiple points of the respective molecules at which the reactants may react, we obtain a mixture of chemical compounds. T'he'exact nature of the manner in which the catalyst influences the reaction is unknown. However, regardless of any theory involved, the use of an activated clay catalyst is an essential feature of our invention, since if the catalyst is omitted, black, insoluble, resinous condensation products are obtained.

The following examples illustrate the preparation of our new addition agent.

Example I.Into an enamel lined reaction vessel, equipped with means for agitation and a reflux condenser, there were placed 170 pounds (1 mol) of p-hydrox'ydiphenyl, 605 pounds (5 mols of N-dimethylaniline, 405 pounds (5 mols) of a 37 per cent by weight aqueous solution of formaldehyde, and 80 pounds of Filtrol (an activated clay) as a catalyst. The mixture was agitated and refluxed at 210 F. for 6 hours, and then while raising the temperature to 280 F., all water. both that added with the formaldehyde and formed in the reaction, was distilled off. The product was then filtered through Celite, a diatomaceous earth filter aid. The product had the following properties:

Specific gravity, 60/60 F Color, NP 3.25 Neutralization No 3.28 pH 7.4

Ezeomple H.An addition agent was prepared by reacting l moi of p-hydroxydiphenyl, 9 mole of formaldehyde and 9 mols of N-dimethylaniline in the presence of 5 per cent by weight of'the total reactants of an activated clay catalyst under the .diphenyl, lhiimethylaniline and formaldehyde in the presence of an activated clay catalyst are excellent addition agents for mineral oil lubricants. They are readily soluble in all types of mineral oils, that is. parailinic, naphthenic or mixed base mineral oils and can be blended with mineral oils in high proportions to form concentrated solutions thereof, which may then be diluted down to the proportions desired in the final mineral oil lubricant composition. As stated, our new addition agents are remarkably effective in inhibiting the oxidative deterioration of mineral oil lubricant compositions. For this purpose small amounts of our new addition agents are generally sufllcient. For example, our addition agents may be added to mineral lubricating oils or greases in minor amounts, say from 0.001 to 1 per cent by weight on the mineral oil or grease, suilicient to inhibit the oxidative deterioration of the oil or grease. Larger amounts of our new addition agents may be used if desired, but it is ordinarily unnecessary to do so.

The following examples illustrate the remarkvable antioxidant eflects of our new addition agents. In the following examples, the base oil and the some oil blended with our new addition agents are subjected to a standard oxidation test which measures. the stability of the oils to oxida: tion. The oxidation test referred to is a standard test described in "ASTM Standards on Petroleum Products and Lubricants. September, 1943, pages conditions set forth in Example I. product 1 had the following properties: r

Specific gravity, /60 F 1.052 Color, NP 1 5.0; Neutralization No 2.0

Specific gravity, sovso" r 1.07s oo oaNP 3.0 Neutralization No 2.8

The condensation products obtained in accordonce with the above disclosure from p-hydroxy- 17-20. Briefly, the test comprises subjecting the oil sample to oxygen at a temperature of C.- (203 1".) in the'presence of water'and an ironcopper catalyst, and determining the time re quired to build up a neutralization number of 2.

The bow of oxygen is maintained at 3 liters perv hour. The remarkably effective stability to ox-' idation of mineral oil lubricant compositions containing our new addition agents is illustrated by the results shown in the following examples.

Example IV .-To a refined turbine oil base there was added 0.5 per cent by weight of the addition agent prepared in accordance. with Example I. A comparison of- Example V.--An improved steam turbine oil was prepared by adding 0.5 per cent by weight of the addition agent prepared in'accordance with Example H to a turbine oil base. A comparison of the base oil and the base oil blended with the antioxidant showed the following results:

. Improved f Base Oil on Gravity, AP! 29.4 29.4 Oxidation Test, ASTM Proposed 13 F. 3 L. Oxygen per Hm Time Oxid m 6055 N outraliatlon No 2. 0 2. 0'-

Our new addition agents also inhibit the oxidative deterioration of mineral oil lubricating greases, and in addition tend to stabilize such gr against separation of the mineral lubrii not be predicted from the nature of the reactants.

eating all contained therein. These effects are shown in the following table, wherein a typical cup grease, prepared by thickening a Texas 011 of 300 S. U. S. at 100 F. with the calcium soap of tallow in the usual manner. and compounded with 0.25 per cent by weight of one of the addition agents of our invention, is compared with the uncompounded identical base grease.

Table I In I Cup Grease Base up Grease Hake-up. per cent by weight:

Cup Grease Base 100 90.75. Additive of Example I 0.25.

on: MeltingPolnt,F.:Hawxhmst. 197 19a Drop ing Point, F.: ASTM m m Dita-42. Flow Point, F.: Method 68, 210 20s.

Ouli (Navy Spec. 14-6-14). Oonsistenc mm.: Braun, 34 34- 82 F., 2. G. Penetration AB'IM D217- 441x11" r., 100 0., a see:

Unworkcd 318 310. Worked 328 330. Water bty distillation, per cent by 1.0 1.0.

weg

Corrosoo ign'lestzMcthodtUA, passes passes.

v Reaction alkaline alkaline. Oxygen Stsbilitg, 176 F.:Hr. 164 500+.

Method 272, uli.

Appearance slight oil separanormal.

on. Odor rancid normal. NeutralizationNo 3.4 0.8.. Ash, gr cent: Nature, Calcium 1.0 1.0.

Oxi

The Oxygen Stability Test, Method 272, Gulf, referred to in the above table is conducted as follows: Twenty grams of the grease to be tested is placed into a suitable bomb capable of withstanding pressure. The bomb is then closed and gaseous oxygen admitted thereto until a. pressure of 100 pounds per square inch is attained. The bomb is then placed in an oil bath maintained at 176 F. After 2 hours the pressure on the bomb is adjusted to 110 pounds per square inch. The pressure is then read every two hours until a pressure drop of 20 pounds per square inch occurs or 500 hours are reached without a pressure drop of 20 pounds per square inch occurring. The test 7 is usually discontinued after 500 hours if the pressure drop specified does not occur. The oxygen stability is expressed as the number of hours taken for the pressure drop 01 20 pounds per square inch to occur or the limit of the test, 500 hours, if the grease retains its oxygen stability by not showing the specified pressure drop.

As may be seen from the above table, a grease not containing our new addition agents had an oxygen stability of 154 hours. In contrast thereto. the grease of our invention ran the full limit of the test, more than 500 hours. It should be noted also that the improved grease showed no separation of oil. At the same time, other desirable properties of the base grease were not substantially affected.

The above examples show the remarkable oxidation stability imparted to mineral oil lubricant compositions by the use of our new addition Thus. condensation products prepared from other functionally similar compounds have been found to be either prooxidant or to show no antioxidant effects whatsoever. For example, we have prepared a condensation product similar to our new addition agent by substituting aniline for N-dimethylaniline. The resulting condensation product was found to be entirely unsuitable for inhibiting the oxidative deterioration of mineral oil lubricant compositions.

Other known addition agents may be incorporated into the lubricant compositions prepared in accordance with our invention. For example, pour point depressants, extreme-pressure agents, bearing corrosion inhibitors and the like may be added,

We claim:

1. The procem of preparing an addition agent for mineral oil lubricants which comprises heating p-hydroxydiphenyl with from 4 to 9 mols of N-dimethylaniline and 4 to 9 mols of-formaldehyde per mol of p-hydroxydiphenyl in the presence of an activated clay catalyst at a temperature not in excess of 350 F. to condense to-- gether the three reactants, and recovering the condensation product. I

2. The process of preparing an addition agent for mineral oil lubricants which comprises heat ing p-hydroxydiphenyl with from 4 to 9 mols of N-dimethylaniline and 4 to 9 mols of formaldehyde per mol of p-hydroxydiphenyl in the presence of 5 to 10 per cent by weight on the total reactants of an activated'clay catalyst at atemperature of from to 280 F. to condense together the three reactants, and recovering the condensation product.

3. The process of preparing an addition agent for mineral oil lubricants which comprises adding an activated clay catalyst, p-hydroxydiphenyl with from 4 to 9 mols of N-dimethylaniline and 4 to 9 mols of formaldehyde per mol of p-hydroxydiphenyl to a mineral lubricating oil, heating the mixture to a temperature not in excess of 350 F. to form a condensation product of the three reactants, and recovering a solution of the condensation product in the mineral lubricating oil.

4. The process of preparing an addition agent for mineral oil lubricants which comprises heating 1 mol of p-hydroxydiphenyl, 5 mols of N- dimethylaniline. and 5 mols of formaldehyde in the presence of an activated clay catalyst at a temperature of from 160 to 280 1". to condense together the three reactants, and recovering the condensation product.

5. The process of preparing an addition agent for mineral oil lubricants which comprises heating 1 mo] of p-hydroxydiphenyl, 9 mols of N-dimethylaniline and 9 mols of formaldehyde in the presence of an activated clay catalyst at a temperature of from 160 to 280 1". to condense together the three reactants, and recovering the condensation product.

8. A non-resinous condensation product of p-hydroxydiphenyl with from 4 to 9 mols of N- dimethylanlline and 4 to 9 mols of formaldehyde per mol of p-hydroxydiphenyl, said product being obtained by the process of claim 1.

7. A non-resinous condensation product of 1 mol of p-hydroxydiphenyl, 5 mols of N-dimethylaniline and 5 mols of formaldehyde, said product being obtained by the process of claim 4.

8. A non-resinous condensation product a! 1 mol of p-hydroxydiphenyl, 9 mols of N-dimeth- 'uctbeingobt'alnedbytheprocessoiclaimb.

O. A lubricant composition comprising a major amount of a mineral lubricating oil, and a minor amount, sumcient to inhibit the oxidative deterioration or said oil at a non-resinous condensation product 0! p-hydroxydiphenyl with from 4 to 0 mols o! N-dimethyianiline and 4 to 9 mols of formaldehyde per mol of p-hydroxydiphenyl, said product being obtained by the process or claim 1.

10. A lubricant composition comprising ama- Jor amount oi. a mineral lubricating oil, and a minor amount, from 0.001 to 1.0 per cent by weight of said 011, or a non-resinous condensation product of p-hydroxydiphenyl with from 4 to 9 mols oi N-dimethylaniline and 4 to 9 mols of formaldehyde per mol of p-hydroxydipbenyi,

'said product being obtained by the process of minor amount, suflicien't to inhibit the oxidative deterioration of said oil of a non-resinous condensation pnoduct or 1 moi of p-hydroxydiphenr1. .5 mols or N-dimethylaniline and ii mols of formaldehyde. being obtained by t he process of claim 4.

'- 13. A lubricant composition comprising a majoramount'oi a mineral lubricating oil, and. a minor amount, aui'iicient to inhibit the o'xidative deterioration of said oil of a non-resinous con- 10 densation product or 1 mol oi! p-hydroxydiphenis TROY L. CANTRELL.

REFERENCES Cm v The iollowingreferences are of record in the 20 file of this patent:

. uNrrnns'rii'rEs PATENTS Number I .v.v.mun et :1... "Her. Dent. Charm, vol. 45, pp. zen-29a: (1am. 

1. THE PROCESS OF PREPARING AN ADDITION AGENT FOR MINERAL OIL LUBRICANTS WHICH COMPRISES HEATING P-HYDROXYDIPHENYL WITH FROM 4 TO 9 MOLS OF N-DIMETHYLANILINE AND 4 TO 9 MOLS OF FORMALDEHYDE PER MOL OF P-HYDROXYDIPHENYL IN THE PRESENCE OF AN ACTIVATED CLAY CATALYST AT A TEMPERATURE NOT IN EXCESS OF 350*F. TO CONDENSE TOGETHER THE THREE REACTANTS, AND RECOVERING THE CONDENSATION PRODUCT. 